- 行业: Printing & publishing
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McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
The plastic deformation of metals, usually at elevated temperatures, into desired shapes by compressive forces exerted through a die. Forging processes are usually classified either by the type of equipment used or by the geometry of the end product. The simplest forging operation is upsetting, which is carried out by compressing the metal between two flat parallel platens. From this simple operation, the process can be developed into more complicated geometries with the use of dies. A number of variables are involved in forging; among major ones are properties of the workpiece and die materials, temperature, friction, speed of deformation, die geometry, and dimensions of the workpiece. One basic principle in forging is the fact that the material flows in the direction of least resistance.
Industry:Science
The nucleus of <sub>1</sub>H<sup>3</sup> (tritium); it is the only known radioactive nuclide belonging to hydrogen. The triton is produced in nuclear reactors by neutron absorption in deuterium (<sub>1</sub>H<sup>2</sup> + <sub>0</sub><i>n</i><sup>1</sup> → <sub>1</sub>H<sup>3</sup> + γ), and decays by β<sup>-</sup> emission to <sub>2</sub>He<sup>3</sup> with a half-life of 12.4 years. The spin of the triton is ½, its magnetic moment is 2.9788 nuclear magnetons, and its mass is 3.01700 atomic mass units. Much of the interest in producing <sub>1</sub>H<sup>3</sup> arises from the fact that the fusion reaction <sub>1</sub>H<sup>3</sup> +<sub>1</sub>H<sup>1</sup> → <sub>2</sub>He<sup>4</sup> releases about 20 MeV of energy. Tritons are also used as projectiles in nuclear bombardment experiments.
Industry:Science
The study of bacteria. While bacteria are different in some important respects from all other kinds of cells, their basic processes of physiology and genetics are the same as in all forms of life. One unusual property of bacteria as a whole is their physiological diversity: Some live in the total absence of oxygen and convert complex carbohydrates to acids and alcohols (fermentation), sulfate to hydrogen sulfide, nitrate to nitrogen gas, and hydrogen plus carbon dioxide to methane gas; others carry out photosynthesis by mechanisms nearly identical to plants; some bacteria can grow and multiply by using energy obtained from oxidation of sulfur, ammonia, hydrogen, or iron while obtaining carbon for cell synthesis from carbon dioxide; and some can obtain their needed nitrogen from the gas in air.
Industry:Science
The role of hybridization (crossing or mating of two plants) in plant speciation (species evolution) has fascinated generations of botanists and evolutionary biologists. Significant progress in understanding this topic has been made recently by cross-disciplinary studies combining quantitative trait locus (QTL) mapping, comparative genomics, ecological fieldwork, chip-based gene expression analysis, and genetic analysis of specific candidate adaptive traits and the genes that encode them. The combination of these approaches has allowed evolutionary biologists to revisit long-standing hypotheses and controversies regarding the role of hybridization in plant evolution, and conceptual developments fueled by this work are beginning to transform our view of how plant species are formed and maintained.
Industry:Science
The subclass within the Chondrichthyes (cartilaginous fishes) that includes the sharks (Euselachii) and the skates and rays (Batoidei). The other subclass within Chondrichthyes, according to traditional classifications, is the Holocephali (chimaera, or ratfishes). It is probable that both groups arose independently during the Silurian or Early Devonian from a group of extinct armored fishes, the Placodermi. The elasmobranchs are distinguished by separate gill openings, amphistylic or hyostylic jaw suspension, and sensory ampullae (of Lorenzini) in the head region. Characters shared with the holocephalans include a variably calcified cartilaginous endoskeleton, placoid scales, urea-retention mechanism, clasper organs in the male for internal fertilization, and the absence of an air (swim) bladder.
Industry:Science
The subdivision of the science of biogeography that is concerned with the detailed description of the distribution of animals and how their past distribution has produced present-day patterns. Scientists in this field attempt to formulate theories that explain the present distributions as elucidated by geography, physiography, climate, ecological correlates (especially vegetation), geological history, the canons of evolutionary theory, and an understanding of the evolutionary relationships of the particular animals under study. Zoogeographical theories are then tested by new data from all germane fields to amplify, verify, or falsify the constructs. In this sense, zoogeography is an integrative science that synthesizes data from other disciplines to apply to the realities of animal distribution.
Industry:Science
The predominant orange pigment of bile. It is the major metabolic breakdown product of heme, the prosthetic group of hemoglobin in red blood cells, and other chromoproteins such as myoglobin, cytochrome, and catalase. The breakdown of hemoglobin from the old red cells takes place at a rapid rate in the reticuloendothelial cells of the liver, spleen, and bone marrow. The steps in this breakdown process include denaturation and removal of the protein globin, oxidation and opening of the tetrapyrole ring, and the removal of iron to form the green pigment biliverdin, which is then reduced to bilirubin by the addition of hydrogen. The formed bilirubin is transported to the liver, probably bound to albumin, where it is conjugated into water-soluble mono- and diglucuronides and to a lesser extent with sulfate.
Industry:Science
The theory and practice of controlling the establishment, composition, and growth of stands of trees for any of the goods (including timber, pulp, energy, fruits, and fodder) and benefits (water, wildlife habitat, microclimate amelioration, and carbon sequestration) that they may be called upon to produce. In practicing silviculture, the forester draws upon knowledge of all natural factors that affect trees growing upon a particular site, and guides the development of the vegetation, which is either essentially natural or only slightly domesticated, to best meet the demands of society in general and ownership in particular. Based on the principles of forest ecology and ecosystem management, silviculture is more the imitation of natural processes of forest growth and development than a substitution for them.
Industry:Science
The process of maintaining one operation in step with another. The commonest example is the electric clock, whose motor rotates at some integral multiple or submultiple of the speed of the alternator in the power station. In television, synchronization is essential in order that the electron beams of receiver picture tubes will be at exactly the same spot on the screen at each instant as is the beam in the television camera tube at the transmitter. Synchronism in television is achieved by transmitting a synchronizing pulse at the end of each scanning line, to make all receivers move simultaneously to the start of the next line. A similar vertical synchronizing pulse is transmitted when the camera beam reaches the bottom of the picture, to make all beams go back to the top for the start of the next field.
Industry:Science
The part of the nervous system that controls visceral functions of the body. This system innervates smooth and cardiac muscle and the glands, and regulates visceral processes including those associated with cardiovascular activity, digestion, metabolism, and thermoregulation. The autonomic nervous system functions primarily at a subconscious level. It is traditionally partitioned into the sympathetic system and the parasympathetic system, based on the region of the brain or spinal cord in which the autonomic nerves have their origin. The sympathetic system is defined by the autonomic fibers that exit thoracic and lumbar segments of the spinal cord. The parasympathetic system is defined by the autonomic fibers that either exit the brainstem via the cranial nerves or exit the sacral segments of the spinal cord.
Industry:Science
